Update high availability documentation with comments from Markus Schiltknecht.
Update high availability documentation with comments from Markus Schiltknecht.

arcivanov/postgres-xl,lintzc/gpdb,yuanzhao/gpdb,lintzc/gpdb,zaksoup/gpdb,50wu/gpdb,kaknikhil/gpdb,yuanzhao/gpdb,techdragon/Postgres-XL,kaknikhil/gpdb,kaknikhil/gpdb,xinzweb/gpdb,cjcjameson/gpdb,cjcjameson/gpdb,ashwinstar/gpdb,50wu/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,yazun/postgres-xl,Chibin/gpdb,kmjungersen/PostgresXL,zaksoup/gpdb,techdragon/Postgres-XL,snaga/postgres-xl,chrishajas/gpdb,jmcatamney/gpdb,edespino/gpdb,greenplum-db/gpdb,yazun/postgres-xl,kaknikhil/gpdb,snaga/postgres-xl,Chibin/gpdb,kaknikhil/gpdb,lisakowen/gpdb,ashwinstar/gpdb,cjcjameson/gpdb,ovr/postgres-xl,chrishajas/gpdb,yuanzhao/gpdb,postmind-net/postgres-xl,adam8157/gpdb,Chibin/gpdb,lintzc/gpdb,cjcjameson/gpdb,royc1/gpdb,Quikling/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,Postgres-XL/Postgres-XL,janebeckman/gpdb,xinzweb/gpdb,greenplum-db/gpdb,zaksoup/gpdb,adam8157/gpdb,snaga/postgres-xl,50wu/gpdb,kaknikhil/gpdb,postmind-net/postgres-xl,techdragon/Postgres-XL,Postgres-XL/Postgres-XL,zaksoup/gpdb,yuanzhao/gpdb,adam8157/gpdb,CraigHarris/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,oberstet/postgres-xl,tpostgres-projects/tPostgres,edespino/gpdb,pavanvd/postgres-xl,Quikling/gpdb,snaga/postgres-xl,50wu/gpdb,chrishajas/gpdb,royc1/gpdb,janebeckman/gpdb,Quikling/gpdb,adam8157/gpdb,arcivanov/postgres-xl,royc1/gpdb,xuegang/gpdb,zeroae/postgres-xl,techdragon/Postgres-XL,adam8157/gpdb,chrishajas/gpdb,kaknikhil/gpdb,ahachete/gpdb,kmjungersen/PostgresXL,techdragon/Postgres-XL,CraigHarris/gpdb,edespino/gpdb,chrishajas/gpdb,0x0FFF/gpdb,zaksoup/gpdb,ovr/postgres-xl,chrishajas/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,tpostgres-projects/tPostgres,lisakowen/gpdb,yuanzhao/gpdb,lintzc/gpdb,Chibin/gpdb,xinzweb/gpdb,50wu/gpdb,xuegang/gpdb,CraigHarris/gpdb,jmcatamney/gpdb,xuegang/gpdb,yuanzhao/gpdb,lintzc/gpdb,kaknikhil/gpdb,jmcatamney/gpdb,rvs/gpdb,greenplum-db/gpdb,Postgres-XL/Postgres-XL,xinzweb/gpdb,arcivanov/postgres-xl,lintzc/gpdb,0x0FFF/gpdb,janebeckman/gpdb,oberstet/postgres-xl,kmjungersen/PostgresXL,rvs/gpdb,50wu/gpdb,edespino/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,royc1/gpdb,rvs/gpdb,xuegang/gpdb,rvs/gpdb,pavanvd/postgres-xl,CraigHarris/gpdb,0x0FFF/gpdb,rvs/gpdb,yuanzhao/gpdb,janebeckman/gpdb,tpostgres-projects/tPostgres,ashwinstar/gpdb,xuegang/gpdb,ovr/postgres-xl,janebeckman/gpdb,oberstet/postgres-xl,lintzc/gpdb,Postgres-XL/Postgres-XL,Quikling/gpdb,ahachete/gpdb,pavanvd/postgres-xl,rvs/gpdb,lisakowen/gpdb,pavanvd/postgres-xl,royc1/gpdb,rvs/gpdb,lisakowen/gpdb,jmcatamney/gpdb,xinzweb/gpdb,ahachete/gpdb,0x0FFF/gpdb,Quikling/gpdb,janebeckman/gpdb,Postgres-XL/Postgres-XL,janebeckman/gpdb,royc1/gpdb,postmind-net/postgres-xl,cjcjameson/gpdb,cjcjameson/gpdb,CraigHarris/gpdb,kaknikhil/gpdb,janebeckman/gpdb,lintzc/gpdb,yuanzhao/gpdb,zeroae/postgres-xl,janebeckman/gpdb,xinzweb/gpdb,arcivanov/postgres-xl,ahachete/gpdb,arcivanov/postgres-xl,xuegang/gpdb,greenplum-db/gpdb,zaksoup/gpdb,rvs/gpdb,zaksoup/gpdb,ashwinstar/gpdb,edespino/gpdb,zeroae/postgres-xl,rvs/gpdb,royc1/gpdb,rvs/gpdb,greenplum-db/gpdb,pavanvd/postgres-xl,Chibin/gpdb,CraigHarris/gpdb,chrishajas/gpdb,oberstet/postgres-xl,janebeckman/gpdb,xuegang/gpdb,Quikling/gpdb,ahachete/gpdb,jmcatamney/gpdb,adam8157/gpdb,edespino/gpdb,royc1/gpdb,jmcatamney/gpdb,chrishajas/gpdb,Quikling/gpdb,ashwinstar/gpdb,kaknikhil/gpdb,Chibin/gpdb,0x0FFF/gpdb,postmind-net/postgres-xl,Chibin/gpdb,Chibin/gpdb,lisakowen/gpdb,jmcatamney/gpdb,ahachete/gpdb,snaga/postgres-xl,kmjungersen/PostgresXL,CraigHarris/gpdb,Chibin/gpdb,cjcjameson/gpdb,yazun/postgres-xl,zeroae/postgres-xl,tpostgres-projects/tPostgres,edespino/gpdb,CraigHarris/gpdb,lisakowen/gpdb,xuegang/gpdb,yazun/postgres-xl,postmind-net/postgres-xl,zeroae/postgres-xl,Chibin/gpdb,oberstet/postgres-xl,ahachete/gpdb,50wu/gpdb,yazun/postgres-xl,0x0FFF/gpdb,0x0FFF/gpdb,ovr/postgres-xl,edespino/gpdb,greenplum-db/gpdb,CraigHarris/gpdb,adam8157/gpdb,arcivanov/postgres-xl,zaksoup/gpdb,Quikling/gpdb,Quikling/gpdb,lisakowen/gpdb,xuegang/gpdb,edespino/gpdb,0x0FFF/gpdb,edespino/gpdb,kmjungersen/PostgresXL,lintzc/gpdb,cjcjameson/gpdb,cjcjameson/gpdb,Quikling/gpdb,adam8157/gpdb,cjcjameson/gpdb,ahachete/gpdb,tpostgres-projects/tPostgres,xinzweb/gpdb,ovr/postgres-xl